The present invention relates to a plug to be anchored in a bore drilled in a support structure.
Anchoring plugs of the type under consideration include an expansible sleeve insertable into the bore of the support structure; an expander body driven into the expansible sleeve by a screw and a bearing member, on which the expansible sleeve is supported and which can be formed, for example by a spacer sleeve. The latter normally lies against a counter bearing of the screw. The counter bearing can be formed by the head of the screw or by a packing washer.
When a spacer sleeve is used as a bearing element an additional sleeve of plastic can be required between the expansible sleeve and the spacer sleeve. The additional sleeve then forms a zone which bulges when compressed so as to ensure that the plug is reliably clamped with an object being fastened to the support structure.
Plugs of another type are also known, which are provided with an expansible sleeve which firmly plugs into the bore drilled in the support structure as the expander body is inserted into the expansible sleeve while the expansible sleeve does not lie against the bearing element.
The use of such anchoring plugs in a tension zone of the anchoring plate requires that the plug would have a considerable expansion quality, in order, as the drill hole enlarges as a result of crack forming, to avoid a reduction in the holding capacity of the plug. Due to he friction acting between the expansible sleeve and the expander body, after the plug has been anchored in the drill hole, in the worst cases, where the drill hole enlarges as a result of cracks formed due to the load acting on the expander body, the expansible sleeve, and therewith the entire plug, can be pulled out of the drill hole, without the enlargement of the drill hole, which is compensated by a further expansion of the plug.